Synergistic modulation of SrTiO3-TiO2 colossal permittivity system by internal lattice defects and phase composition: Experimental and theoretical investigations

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The SrTiO3–TiO2 composite ceramics with different contents of La doping were fabricated by traditional solid-state sintering methods. The performance of the colossal permittivity ceramics was enhanced by the synergistic design of the internal defect structure and phase composition. When the doping content is 2%, SrTiO3–TiO2 composite ceramics possessed a colossal permittivity (ԑr ∼ 1.1 × 105), low dielectric loss (tanδ ∼ 0.050) and favorable thermal stability (−70 °C-150 °C, ΔC/C25°C ≤ ±15%). Phase structure analysis suggested that a TiO2 secondary phase was induced at the grain boundaries of SrTiO3 phase with the addition of La3+ ions. XPS and dielectric behavior analyses revealed that oxygen vacancies and lattice defects formed by inhomogeneous ion-doping act to modulate the dielectric behavior in ceramics. The IBLC interfacial effects in relation to semiconductor grains and insulation grain boundaries are the main contributors to the colossal permittivity (CP) properties of ceramics, and the contribution of the IBLC effects becomes more prominent with increasing doping content. On the basis of first-principles analysis, the ceramic lattice undergoes severe deformation when the La content is increased, and the gathering of electrons at oxygen vacancies and defects is evident. As a result, it leads to enhanced grain semiconducting properties and interfacial effects, which facilitate colossal permittivity and low dielectric loss for ceramics. The results are prospective in the application of CP ceramics.